<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <script src="https://cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.js"></script>
  <title>Document</title>
</head>

<body>
  <div id="App">
    <div class="box" :class="{active:isActive}"></div>
    <button @click="isActive = !isActive">切换</button>
  </div>
  <script>
    const vm = new Vue({
      el: '#App',
      data () {
        return {
          isActive: true,
          className: {
            red: true,
            blue: false,
            pink: false
          }
        }
      }
    })
  </script>
</body>

<style>
  .box {
    width: 100px;
    height: 100px;
    background-color: gold;
    transition: all 300ms ease-in-out;
  }

  .active {
    background-color: pink;
    width: 200px;
    height: 200px;
    transition: all 300ms ease-in-out;
  }
</style>

</html>